Continuous Glucose Monitoring System and Methods of Use

ABSTRACT

A continuous glucose monitoring system including a sensor configured to detect one or more glucose levels, a transmitter operatively coupled to the sensor, the transmitter configured to receive the detected one or more glucose levels, the transmitter further configured to transmit signals corresponding to the detected one or more glucose levels, and a receiver operatively coupled to the transmitter configured to receive transmitted signals corresponding to the detected one or more glucose levels, and methods thereof, are disclosed. In one aspect, the transmitter may be configured to transmit a current data point and at least one previous data point, the current data point and the at least one previous data point corresponding to the detected one or more glucose levels.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/481,256 filed May 25, 2012, now U.S. Pat. No. 8,622,903,which is a continuation of U.S. patent application Ser. No. 12/902,138filed Oct. 11, 2010, now U.S. Pat. No. 8,187,183, which is acontinuation of U.S. patent application Ser. No. 10/745,878 filed Dec.26, 2003, now U.S. Pat. No. 7,811,231, which claims the benefit of U.S.Provisional Application No. 60/437,374 filed Dec. 31, 2002, entitled“Continuous Glucose Monitoring System and Methods of Use”, thedisclosures of each of which are incorporated herein by reference forall purposes.

BACKGROUND

The present invention relates to continuous glucose monitoring systems.More specifically, the present invention relates to an in-vivocontinuous glucose monitoring system which detects glucose levelscontinuously and transfers the detected glucose level information atpredetermined time intervals to data processing devices for monitoring,diagnosis and analysis.

SUMMARY

A continuous glucose monitoring system in accordance with one embodimentof the present invention includes a sensor configured to detect one ormore glucose levels, a transmitter operatively coupled to the sensor,the transmitter configured to receive the detected one or more glucoselevels, the transmitter further configured to transmit signalscorresponding to the detected one or more glucose levels, a receiveroperatively coupled to the transmitter configured to receive transmittedsignals corresponding to the detected one or more glucose levels, wherethe transmitter is configured to transmit a current data point and atleast one previous data point, the current data point and the at leastone previous data point corresponding to the detected one or moreglucose levels.

The receiver may be operatively coupled to the transmitter via an RFcommunication link, and further, configured to decode the encodedsignals received from the transmitter.

In one embodiment, the transmitter may be configured to periodicallytransmit a detected and processed glucose level from the sensor to thereceiver via the RF data communication link. In one embodiment, thetransmitter may be configured to sample four times every second toobtain 240 data points for each minute, and to transmit at a rate of onedata point (e.g., an average value of the 240 sampled data points forthe minute) per minute to the receiver.

The transmitter may be alternately configured to transmit three datapoints per minute to the receiver, the first data point representing thecurrent sampled data, and the remaining two transmitted data pointsrepresenting the immediately past two data points previously sent to thereceiver. In this manner, in the case where the receiver does notsuccessfully receive the sampled data from the transmitter, at thesubsequent data transmission, the immediately prior transmitted data isreceived by the receiver. Thus, even with a faulty connection betweenthe transmitter and the receiver, or a failed RF data link, the presentapproach ensures that missed data points may be ascertained from thesubsequent data point transmissions without retransmission of the misseddata points to the receiver.

The transmitter may be configured to encode the detected one or moreglucose levels received from the sensor to generate encoded signals, andto transmit the encoded signals to the receiver. In one embodiment, thetransmitter may be configured to transmit the encoded signals to thereceiver at a transmission rate of one data point per minute. Further,the transmitter may be configured to transmit the current data point andthe at least one previous data points in a single transmission perminute to the receiver. In one aspect, the current data point maycorrespond to a current glucose level, and where the at least oneprevious data point may include at least two previous data pointscorresponding respectively to at least two consecutive glucose levels,the one of the at least two consecutive glucose levels immediatelypreceding the current glucose level.

In a further embodiment, the receiver may include an output unit foroutputting the received transmitted signals corresponding to one or moreglucose levels. The output unit may include a display unit fordisplaying data corresponding to the one or more glucose levels, wherethe display unit may include one of a LCD display, a cathode ray tubedisplay, and a plasma display.

The displayed data may include one or more of an alphanumericrepresentation corresponding to the one or more glucose levels, agraphical representation of the one or more glucose levels, and athree-dimensional representation of the one or more glucose levels.Moreover, the display unit may be configured to display the datacorresponding to the one or more glucose levels substantially in realtime.

Further, the output unit may include a speaker for outputting an audiosignal corresponding to the one or more glucose levels.

In yet a further embodiment, the receiver may be configured to store anidentification information corresponding to the transmitter.

The receiver may be further configured to perform a time hoppingprocedure for synchronizing with the transmitter. Alternatively, thereceiver may be configured to synchronize with the transmitter based onthe signal strength detected from the transmitter, where the detectedsignal strength exceeds a preset threshold level.

The transmitter in one embodiment may be encased in a substantiallywater-tight housing to ensure continuous operation even in the situationwhere the transmitter is in contact with water.

Furthermore, the transmitter may be configured with a disable switchwhich allows the user to temporarily disable the transmission of data tothe receiver when the user is required to disable electronic devices,for example, when aboard an airplane. In another embodiment, thetransmitter may be configured to operate in an additional third state(such as under Class B radiated emissions standard) in addition to theoperational state and the disable state discussed above, so as to allowlimited operation while aboard an airplane yet still complying with theFederal Aviation Administration (FAA) regulations. Additionally, thedisable switch may also be configured to switch the transmitter betweenvarious operating modes such as fully functional transmission mode,post-manufacture sleep mode, and so on. In this manner, the power supplyfor the transmitter is optimized for prolonged usage by effectivelymanaging the power usage.

Furthermore, the transmitter may be configured to transmit the data tothe receiver in predetermined data packets, encoded, in one embodiment,using Reed Solomon encoding, and transmitted via the RF communicationlink. Additionally, in a further aspect of the present invention, the RFcommunication link between the transmitter and the receiver of thecontinuous glucose monitoring system may be implemented using a lowcost, off the shelf remote keyless entry (RKE) chip set.

The receiver in an additional embodiment may be configured to perform,among others, data decoding, error detection and correction (using, forexample, forward error correction) on the encoded data packets receivedfrom the transmitter to minimize transmission errors such as transmitterstabilization errors and preamble bit errors resulting from noise. Thereceiver is further configured to perform a synchronized time hoppingprocedure with the transmitter to identify and synchronize with thecorresponding transmitter for data transmission.

Additionally, the receiver may include a graphical user interface (GUI)for displaying the data received from the transmitter for the user. TheGUI may include a liquid crystal display (LCD) with backlighting featureto enable visual display in dark surroundings. The receiver may alsoinclude an output unit for generating and outputting audible signalalerts for the user, or placing the receiver in a vibration mode foralerting the user by vibrating the receiver.

More specifically, in a further aspect, the receiver may be configuredto, among others, display the received glucose levels on a displaysection of the receiver either real time or in response to user request,and provide visual (and/or auditory) notification to the user of thedetected glucose levels being monitored. To this end, the receiver isconfigured to identify the corresponding transmitter from which it is toreceive data via the RF data link, by initially storing theidentification information of the transmitter, and performing a timehopping procedure to isolate the data transmission from the transmittercorresponding to the stored identification information and thus tosynchronize with the transmitter. Alternatively, the receiver may beconfigured to identify the corresponding transmitter based on the signalstrength detected from the transmitter, determined to exceed a presetthreshold level.

A method in accordance with one embodiment of the present inventionincludes the steps of receiving an identification informationcorresponding to a transmitter, detecting data within a predetermined RFtransmission range, determining whether the detected data is transmittedfrom the transmitter, decoding the detected data, and generating anoutput signal corresponding to the decoded data.

In one embodiment, the step of determining whether the detected datatransmission is transmitted from the transmitter may be based on thereceived identification information. In another embodiment, the step ofdetermining whether the detected data transmission is transmitted fromthe transmitter may be based on the signal strength and duration of thedetected data within the predetermined RF transmission range.

In a further embodiment, the step of decoding may also include the stepof performing error correction on the decoded data. Moreover, the stepof decoding may include the step of performing Reed-Solomon decoding onthe detected data.

In the manner described, the present invention provides a continuousglucose monitoring system that is simple to use and substantiallycompact so as to minimize any interference with the user's dailyactivities. Furthermore, the continuous glucose monitoring system may beconfigured to be substantially water-resistant so that the user mayfreely bathe, swim, or enjoy other water related activities while usingthe monitoring system. Moreover, the components comprising themonitoring system including the transmitter and the receiver areconfigured to operate in various modes to enable power savings, and thusenhancing post-manufacture shelf life.

INCORPORATION BY REFERENCE

Applicants herein incorporate by reference application Ser. No.09/753,746 filed on Jan. 2, 2001, and issued on May 6, 2003 as U.S. Pat.No. 6,560,471, entitled “Analyte Monitoring Device and Methods of Use”assigned to the Assignee of the present application for all purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a continuous glucose monitoring system in accordancewith one embodiment of the present invention;

FIG. 2 is a block diagram of the transmitter of the continuous glucosemonitoring system shown in FIG. 1 in accordance with one embodiment ofthe present invention;

FIG. 3 is a block diagram of the receiver of the continuous glucosemonitoring system shown in FIG. 1 in accordance with one embodiment ofthe present invention;

FIG. 4 illustrates a data packet of the transmitter of the continuousglucose monitoring system shown in FIG. 1 in accordance with oneembodiment of the present invention;

FIGS. 5A, 5B and 5C illustrate a data packet table for Reed-Solomonencoding in the transmitter, a depadded data table, and a link prefixtable, respectively, in accordance with one embodiment of the continuousglucose monitoring system of FIG. 1; and

FIG. 6 is a flowchart illustrating the time hopping procedure for thereceiver of the continuous glucose monitoring system shown in FIG. 1 inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a continuous glucose monitoring system 100 inaccordance with one embodiment of the present invention. In suchembodiment, the continuous glucose monitoring system 100 includes asensor 101, a transmitter 102 coupled to the sensor 101, and a receiver104 which is configured to communicate with the transmitter 102 via acommunication link 103. The receiver 104 may be further configured totransmit data to a data processing terminal 105 for evaluating the datareceived by the receiver 104. Only one sensor 101, transmitter 102,communication link 103, receiver 104, and data processing terminal 105are shown in the embodiment of the continuous glucose monitoring system100 illustrated in FIG. 1. However, it will be appreciated by one ofordinary skill in the art that the continuous glucose monitoring system100 may include one or more sensor 101, transmitter 102, communicationlink 103, receiver 104, and data processing terminal 105, where eachreceiver 104 is uniquely synchronized with a respective transmitter 102.

In one embodiment of the present invention, the sensor 101 is physicallypositioned on the body of a user whose glucose is being monitored. Theterm user as used herein is intended to include humans, animals, as wellas any other who might benefit from the use of the glucose monitoringsystem 100. The sensor 101 is configured to continuously sample theglucose level of the user and convert the sampled glucose level into acorresponding data signal for transmission by the transmitter 102. Inone embodiment, the transmitter 102 is mounted on the sensor 101 so thatboth devices are positioned on the user's body. The transmitter 102performs data processing such as filtering and encoding on data signals,each of which corresponds to a sampled glucose level of the user, fortransmission to the receiver 104 via the communication link 103.

In one embodiment, the continuous glucose monitoring system 100 isconfigured as a one-way RF communication path from the transmitter 102to the receiver 104. In such embodiment, the transmitter 102 transmitsthe sampled data signals received from the sensor 101 withoutacknowledgement from the receiver 104 that the transmitted sampled datasignals have been received. For example, the transmitter 102 may beconfigured to transmit the encoded sampled data signals at a fixed rate(e.g., at one minute intervals) after the completion of the initialpower on procedure. Likewise, the receiver 104 may be configured todetect such transmitted encoded sampled data signals at predeterminedtime intervals.

As discussed in further detail below, in one embodiment of the presentinvention the receiver 104 includes two sections. The first section isan analog interface section that is configured to communicate with thetransmitter 102 via the communication link 103. In one embodiment, theanalog interface section may include an RF receiver and an antenna forreceiving and amplifying the data signals from the transmitter 102,which are thereafter, demodulated with a local oscillator and filteredthrough a band-pass filter. The second section of the receiver 104 is adata processing section which is configured to process the data signalsreceived from the transmitter 102 such as by performing data decoding,error detection and correction, data clock generation, and data bitrecovery.

In operation, upon completing the power-on procedure, the receiver 104is configured to detect the presence of the transmitter 102 within itsrange based on the strength of the detected data signals received fromthe transmitter 102. For example, in one embodiment, the receiver 104 isconfigured to detect signals whose strength exceeds a predeterminedlevel to identify the transmitter 102 from which the receiver 104 is toreceive data. Alternatively, the receiver 104 in a further embodimentmay be configured to respond to signal transmission for a predeterminedtransmitter identification information of a particular transmitter 102such that, rather than detecting the signal strength of a transmitter102 to identify the transmitter, the receiver 104 may be configured todetect transmitted signal of a predetermined transmitter 102 based onthe transmitted transmitter identification information corresponding tothe pre-assigned transmitter identification information for theparticular receiver 104.

In one embodiment, the identification information of the transmitters102 includes a 16-bit ID number. In an alternate embodiment, the IDnumber may be a predetermined length including a 24-bit ID number or a32-bit ID number. Further, any other length ID number may also be used.Thus, in the presence of multiple transmitters 102, the receiver 104will only recognize the transmitter 102 which corresponds to the storedidentification information. Data signals transmitted from the othertransmitters within the range of the receiver 104 are considered invalidsignals.

Referring again to FIG. 1, where the receiver 104 determines thecorresponding transmitter 102 based on the signal strength of thetransmitter 102, when the receiver 104 is initially powered-on, thereceiver 104 is configured to continuously sample the signal strength ofthe data signals received from the transmitters within its range. If thesignal strength of the data signals meets or exceeds the signal strengththreshold level and the transmission duration threshold level, thereceiver 104 returns a positive indication for the transmitter 102transmitting the data signals. That is, in one embodiment, the receiver104 is configured to positively identify the transmitter 102 after onedata signal transmission. Thereafter, the receiver 104 is configured todetect positive indications for three consecutive data signaltransmissions for a predetermined time period. At such point, afterthree consecutive transmissions, the transmitter 102 is fullysynchronized with the receiver 104.

Upon identifying the appropriate transmitter 102, the receiver 104begins a decoding procedure to decode the received data signals. In oneembodiment, a sampling clock signal may be obtained from the preambleportion of the received data signals. The decoded data signals, whichinclude fixed length data fields, are then sampled with the samplingclock signal. In one embodiment of the present invention, based on thereceived data signals and the time interval between each of the threedata signal transmissions, the receiver 104 determines the wait timeperiod for receiving the next transmission from the identified andsynchronized transmitter 102. Upon successful synchronization, thereceiver 104 begins receiving from the transmitter 102 data signalscorresponding to the user's detected glucose level. As described infurther detail below, the receiver 104 in one embodiment is configuredto perform synchronized time hopping with the corresponding synchronizedtransmitter 102 via the communication link 103 to obtain the user'sdetected glucose level.

Referring yet again to FIG. 1, the data processing terminal 105 mayinclude a personal computer, a portable computer such as a laptop or ahandheld device (e.g., personal digital assistants (PDAs)), and thelike, each of which is configured for data communication with thereceiver via a wired or a wireless connection. Additionally, the dataprocessing terminal 105 may further be connected to a data network (notshown) for storing, retrieving and updating data corresponding to thedetected glucose level of the user.

FIG. 2 is a block diagram of the transmitter 102 of the continuousglucose monitoring system 100 in accordance with one embodiment of thepresent invention. The transmitter 102 includes an analog interface 201configured to communicate with the sensor 101 (FIG. 1), a user input202, and a temperature detection section 203, each of which isoperatively coupled to a transmitter processor 204 such as a centralprocessing unit (CPU). Further shown in FIG. 2 are a transmitter serialcommunication section 205 and an RF transmitter 206, each of which isalso operatively coupled to the transmitter processor 204. Moreover, apower supply 207 is also provided in the transmitter 102 to provide thenecessary power for the transmitter 102. Additionally, as can be seenfrom the Figure, clock 208 is provided to, among others, supply realtime information to the transmitter processor 204.

In one embodiment, a unidirectional input path is established from thesensor 101 (FIG. 1) and/or manufacturing and testing equipment to theanalog interface 201, while a unidirectional output is established fromthe output of the RF transmitter 206. In this manner, a data path isshown in FIG. 2 between the aforementioned unidirectional input andoutput via a dedicated link 209 from the analog interface 201 to serialcommunication section 205, thereafter to the processor 204, and then tothe RF transmitter 206. As such, in one embodiment, through the datapath described above, the transmitter 102 is configured to transmit tothe receiver 104 (FIG. 1), via the communication link 103 (FIG. 1),processed and encoded data signals received from the sensor 101 (FIG.1). Additionally, the unidirectional communication data path between theanalog interface 201 and the RF transmitter 206 discussed above allowsfor the configuration of the transmitter 102 for operation uponcompletion of the manufacturing process as well as for directcommunication for diagnostic and testing purposes.

Referring back to FIG. 2, the user input 202 includes a disable devicethat allows the operation of the transmitter 102 to be temporarilydisabled, such as, by the user wearing the transmitter 102. In analternate embodiment, the disable device of the user input 202 may beconfigured to initiate the power-up procedure of the transmitter 102.

As discussed above, the transmitter processor 204 is configured totransmit control signals to the various sections of the transmitter 102during the operation of the transmitter 102. In one embodiment, thetransmitter processor 204 also includes a memory (not shown) for storingdata such as the identification information for the transmitter 102, aswell as the data signals received from the sensor 101. The storedinformation may be retrieved and processed for transmission to thereceiver 104 under the control of the transmitter processor 204.Furthermore, the power supply 207 may include a commercially availablebattery pack.

The physical configuration of the transmitter 102 is designed to besubstantially water resistant, so that it may be immersed in non-salinewater for a brief period of time without degradation in performance.Furthermore, in one embodiment, the transmitter 102 is designed so thatit is substantially compact and light-weight, not weighing more than apredetermined weight such as, for example, approximately 18 grams.Furthermore, the dimensions of the transmitter 102 in one embodimentincludes 52 mm in length, 30 mm in width and 12 mm in thickness. Suchsmall size and weight enable the user to easily carry the transmitter102.

The transmitter 102 is also configured such that the power supplysection 207 is capable of providing power to the transmitter for aminimum of three months of continuous operation after having been storedfor 18 months in a low-power (non-operating) mode. In one embodiment,this may be achieved by the transmitter processor 204 operating in lowpower modes in the non-operating state, for example, drawing no morethan approximately 1 μA. Indeed, in one embodiment, the final stepduring the manufacturing process of the transmitter 102 places thetransmitter 102 in the lower power, non-operating state (i.e.,post-manufacture sleep mode). In this manner, the shelf life of thetransmitter 102 may be significantly improved.

Referring again to FIG. 2, the analog interface 201 of the transmitter102 in one embodiment includes a sensor interface (not shown) configuredto physically couple to the various sensor electrodes (such as, forexample, working electrode, reference electrode, counter electrode, (notshown)) of the sensor 101 (FIG. 1) of the monitoring system 100. Theanalog interface section 201 further includes a potentiostat circuit(not shown) which is configured to generate the Poise voltage determinedfrom the current signals received from the sensor electrodes. Inparticular, the Poise voltage is determined by setting the voltagedifference between the working electrode and the reference electrode(i.e., the offset voltage between the working electrode and thereference electrode of the sensor 101). Further, the potentiostatcircuit also includes a transimpedance amplifier for converting thecurrent signal on the working electrode into a corresponding voltagesignal proportional to the current. The signal from the potentiostatcircuit is then low pass filtered with a predetermined cut-off frequencyto provide anti-aliasing, and thereafter, passed through a gain stage toprovide sufficient gain to allow accurate signal resolution detectedfrom the sensor 101 for analog-to-digital conversion and encoding fortransmission to the receiver 104.

Referring yet again to FIG. 2, the temperature detection section 203 ofthe transmitter 102 is configured to monitor the temperature of the skinnear the sensor insertion site. The temperature reading is used toadjust the glucose readings obtained from the analog interface 201. Asdiscussed above, the input section 202 of the transmitter 102 includesthe disable device which allows the user to temporarily disable thetransmitter 102 such as for, example, to comply with the FAA regulationswhen aboard an aircraft. Moreover, in a further embodiment, the disabledevice may be further configured to interrupt the transmitter processor204 of the transmitter 102 while in the low power, non-operating mode toinitiate operation thereof.

The RF transmitter 206 of the transmitter 102 may be configured foroperation in the frequency band of 315 MHz to 322 MHz, for example, inthe United States. Further, in one embodiment, the RF transmitter 206 isconfigured to modulate the carrier frequency by performing FrequencyShift Keying and Manchester encoding. In one embodiment, the datatransmission rate is 19,200 symbols per second, with a minimumtransmission range for communication with the receiver 104.

FIG. 3 is a block diagram of the receiver 104 of the continuous glucosemonitoring system 100 in accordance with one embodiment of the presentinvention. Referring to FIG. 3, the receiver 104 includes a bloodglucose test strip interface 301, an RF receiver 302, an input 303, atemperature detection section 304, and a clock 305, each of which isoperatively coupled to a receiver processor 307. As can be further seenfrom the Figure, the receiver 104 also includes a power supply 306operatively coupled to a power conversion and monitoring section 308.Further, the power conversion and monitoring section 308 is also coupledto the receiver processor 307. Moreover, also shown are a receiverserial communication section 309, and an output 310, each operativelycoupled to the receiver processor 307.

In one embodiment, the test strip interface 301 includes a glucose leveltesting portion to receive a manual insertion of a glucose testingstrip, and thereby determine and display the glucose level of thetesting strip on the output 310 of the receiver 104. This manual testingof glucose can be used to calibrate sensor 101. The RF receiver 302 isconfigured to communicate, via the communication link 103 (FIG. 1) withthe RF transmitter 206 of the transmitter 102, to receive encoded datasignals from the transmitter 102 for, among others, signal mixing,demodulation, and other data processing. The input 303 of the receiver104 is configured to allow the user to enter information into thereceiver 104 as needed. In one aspect, the input 303 may include one ormore keys of a keypad, a touch-sensitive screen, or a voice-activatedinput command unit. The temperature detection section 304 is configuredto provide temperature information of the receiver 104 to the receiverprocessor 307, while the clock 305 provides, among others, real timeinformation to the receiver processor 307.

Each of the various components of the receiver 104 shown in FIG. 3 arepowered by the power supply 306 which, in one embodiment, includes abattery. Furthermore, the power conversion and monitoring section 308 isconfigured to monitor the power usage by the various components in thereceiver 104 for effective power management and to alert the user, forexample, in the event of power usage which renders the receiver 104 insub-optimal operating conditions. An example of such sub-optimaloperating condition may include, for example, operating the vibrationoutput mode (as discussed below) for a period of time thus substantiallydraining the power supply 306 while the processor 307 (thus, thereceiver 104) is turned on. Moreover, the power conversion andmonitoring section 308 may additionally be configured to include areverse polarity protection circuit such as a field effect transistor(FET) configured as a battery activated switch.

The serial communication section 309 in the receiver 104 is configuredto provide a bi-directional communication path from the testing and/ormanufacturing equipment for, among others, initialization, testing, andconfiguration of the receiver 104. Serial communication section 309 canalso be used to upload data to a computer, such as time-stamped bloodglucose data. The communication link with an external device (not shown)can be made, for example, by cable, infrared (IR) or RF link. The output310 of the receiver 104 is configured to provide, among others, agraphical user interface (GUI) such as a liquid crystal display (LCD)for displaying information. Additionally, the output 310 may alsoinclude an integrated speaker for outputting audible signals as well asto provide vibration output as commonly found in handheld electronicdevices, such as mobile telephones presently available. In a furtherembodiment, the receiver 104 also includes an electro-luminescent lampconfigured to provide backlighting to the output 310 for output visualdisplay in dark ambient surroundings.

Referring back to FIG. 3, the receiver 104 in one embodiment may alsoinclude a storage section such as a programmable, non-volatile memorydevice as part of the processor 307, or provided separately in thereceiver 104, operatively coupled to the processor 307. The processor307 is further configured to perform Manchester decoding as well aserror detection and correction upon the encoded data signals receivedfrom the transmitter 102 via the communication link 103.

In conjunction with FIGS. 4, 5A, 5B and 5C, a description is provided ofa data packet from the transmitter 102 to the receiver 104 via thecommunication link 103.

FIG. 4 illustrates a data pack from the transmitter 102 (FIG. 1) inaccordance with one embodiment of the present invention. Referring toFIG. 4, each data packet from the transmitter 102 includes 13 bytes asshown in the Figure. For example, the first byte (zero byte) includesthe transmitter 102 identification information (“Tx ID”), while thethird byte (byte two) provides transmitter status information, where ahigh nibble (byte) indicates an operating mode status, while a lownibble indicates a non-operating mode. In this manner, the signalsreceived from the sensor 101 are packed into 13-byte data packs, fortransmission to the receiver 104.

FIGS. 5A, 5B and 5C illustrate a data packet table for Reed-Solomonencoding in the transmitter, a depadded data table, and a link prefixtable, respectively, in accordance with one embodiment of the continuousglucose monitoring system of FIG. 1. Referring to FIG. 5A, it can beseen that the Reed Solomon encoded data block contents include 13 bytesof packed data (FIG. 4), one byte of the middle significant bit of thetransmitter identification information (Tx ID), one byte of the mostsignificant bit of the transmitter identification information, 232 bytesof zero pads, 8 bytes of parity symbols, to comprise a total of 255bytes. In one embodiment, the Reed Solomon encode procedure at thetransmitter 102 uses 8 bit symbols for a 255 symbol block to generate 8parity symbols. Thereafter, the transmitter 102 is configured to removethe 232 bytes of zero pads, resulting in the 21 bytes of depadded datablock including the 13 bytes of packed data as well as the 8 bytes ofthe parity symbols as shown in FIG. 5B.

Thereafter, a link prefix is added to the depadded data block tocomplete the data packet for transmission to the receiver 104. The linkprefix allows the receiver 104 to synchronize with the transmitter 102as described in further detail below. More specifically, as shown inFIG. 5C, the transmitter 102 is configured to add 4 bytes of link prefix(0×00, 0×00, 0×12, and 0×34) to the 21 bytes of depadded data block toresult in 25 bytes of data packet. Once powered up and enabled inoperational mode, the transmitter 102 is configured to transmit the 25byte data packet once every minute. More specifically, the transmitter102 is configured to Manchester encode the data at 2 bits per data bit(0=10; 1=01), and transmit the Manchester bits at 19,200 symbols persecond. The transmitter 102 is configured to transmit the data packetswith the most significant bit of byte zero first.

FIG. 6 is a flowchart illustrating the time hopping procedure for thereceiver of the continuous glucose monitoring system shown in FIG. 1 inaccordance with one embodiment of the present invention.

Referring to FIG. 6, upon completing the power up procedure as discussedabove, the receiver 104 listens for the presence of a transmitter withinthe RF communication link range. At step 601, when the transmitter 102is detected within the RF communication link range, the receiver 104 isconfigured to receive and store the identification informationcorresponding to the detected transmitter 102. Thereafter, at step 602,the receiver 104 is configured to detect (or sample) data transmissionwithin its RF communication range. In one aspect, the receiver 104 isconfigured to identify a positive data transmission upon ascertainingthat the data transmission is above a predetermined strength level for agiven period of time (for example, receiving three separate data signalsabove the predetermined strength level from the transmitter 102 at oneminute intervals over a period of five minutes).

At step 603, the receiver 104 is configured to determine whether thedetected signals within the RF communication range is transmitted fromthe transmitter 102 having the transmitter identification informationstored in the receiver 104. If it is determined at step 603 that thedetected data transmission at step 602 does not originate from thetransmitter with the stored transmitter identification information, thenthe procedure returns to step 602 and waits for the detection of thenext data transmission.

On the other hand, if at step 603 it is determined that the detecteddata transmission is from the transmitter 102 corresponding to thestored transmitter identification information, then at step 604, thereceiver proceeds with decoding the received data and performing errorcorrection thereon. In one embodiment, the receiver is configured toperform Reed-Solomon decoding, where the transmitted data received bythe receiver is encoded with Reed-Solomon encoding. Furthermore, thereceiver is configured to perform forward error correction to minimizedata error due to, for example, external noise, transmission noise andso on.

Referring back to FIG. 6, after decoding and error correcting thereceived data, the receiver 104 at step 605 generates output datacorresponding to the decoded error corrected data received from thetransmitter 102, and thereafter, at step 606, the receiver 104 outputsthe generated output data for the user as a real time display of theoutput data, or alternatively, in response to the user operationrequesting the display of the output data. Additionally, beforedisplaying the output data for the user, other pre-processing proceduresmay be performed on the output data to for example, smooth out theoutput signals. In one aspect, the generated output data may include avisual graphical output displayed on the graphical user interface of thereceiver. Alternatively, the output data may be numerically displayedrepresenting the corresponding glucose level.

Referring now to FIGS. 4 and 6, the time hopping procedure of oneembodiment is described. More specifically, since more than onetransmitter 102 may be within the receiving range of a particularreceiver 104, and each transmitting data every minute on the samefrequency, transmitter units 102 are configured to transmit data packetsat different times to avoid co-location collisions (that is, where oneor more receivers 104 cannot discern the data signals transmitted bytheir respective associated transmitter units 102 because they aretransmitting at the same time).

In one aspect, transmitter 102 is configured to transmit once everyminute randomly in a window of time of plus or minus 5 seconds (i.e., ittime hops.) To conserve power, receiver 104 does not listen for itsassociated transmitter 102 during the entire 10 second receive window,but only at the predetermined time it knows the data packet will becoming from the corresponding transmitter 102. In one embodiment, the 10second window is divided into 400 different time segments of 25milliseconds each. Before each RF transmission from the transmitter 102takes place, both the transmitter 102 and the receiver 104 is configuredto recognize in which one of the 400 time segments the data transmissionwill occur (or in which to start, if the transmission time exceeds 25milliseconds). Accordingly, receiver 104 only listens for a RFtransmission in a single 25 millisecond time segment each minute, whichvaries from minute to minute within the 10 second time window.

Moreover, each transmitter 102 is configured to maintain a “master time”clock that the associated receiver unit 104 may reference to each minute(based on the time of transmission and known offset for that minute). Acounter also on the transmitter 102 may be configured to keep track of avalue “Tx Time” that increments by 1 each minute, from 0 to 255 and thenrepeats. This Tx Time value is transmitted in the data packet eachminute, shown as Byte 1 in FIG. 4. Using the Tx Time value and thetransmitter's unique identification information (TX ID, shown as Byte 0in FIG. 4), both the transmitter 102 and the receiver 104 can calculatewhich of the 400 time segments will be used for the subsequenttransmission. In one embodiment, the function that is used to calculatethe offset from the master clock 1-minute tick is a pseudo-random numbergenerator that uses both the Tx Time and the TX ID as seed numbers.Accordingly, the transmission time varies pseudo-randomly within the 10second window for 256 minutes, and then repeats the same time hoppingsequence again for that particular transmitter 102.

In the manner described above, in accordance with one embodiment of thepresent invention, co-location collisions may be avoided with theabove-described time hopping procedure. That is, in the event that twotransmitters interfere with one another during a particulartransmission, they are not likely to fall within the same time segmentin the following minute. As previously described, three glucose datepoints are transmitted each minute (one current and tworedundant/historical), so collisions or other interference must occurfor 3 consecutive data transmissions for data to be lost. In one aspect,when a transmission is missed, the receiver 104 may be configured tosuccessively widen its listening window until normal transmissions fromthe respective transmitter 102 resume. Under this approach, thetransmitter listens for up to 70 seconds when first synchronizing with atransmitter 102 so it is assured of receiving a transmission fromtransmitter 102 under normal conditions.

Various other modifications and alterations in the structure and methodof operation of this invention will be apparent to those skilled in theart without departing from the scope and spirit of the invention.Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiments. It isintended that the following claims define the scope of the presentinvention and that structures and methods within the scope of theseclaims and their equivalents be covered thereby.

What is claimed is:
 1. An analyte monitoring system, comprising: asensor configured to generate signals corresponding to monitored analytelevel in interstitial fluid; and sensor electronics operatively coupledto the sensor and configured to process the generated signals to formdata packets associated with the generated signals from the sensor, anda temperature sensor configured to monitor temperature associated withthe sensor, wherein the monitored temperature is used to adjust theprocessed generated signals; wherein the sensor electronics includesprogramming to communicate the data packets with each datacommunication, the data packets including a current data point thatcorresponds to an analyte level of a current time period and at leastone previous data point that corresponds to at least one analyte levelof at least one previous time period, and further wherein if the currentdata point is not successfully received, at a subsequent datacommunication, the current data point and the at least one previous datapoint are re-transmitted with a new current data point.
 2. The system ofclaim 1, wherein the at least one previous data point includes twoconsecutive data points that corresponds to the monitored analyte levelof two consecutive previous time periods, one of the two consecutiveprevious time periods immediately preceding the current time period. 3.The system of claim 1, wherein the current data point is received andascertained from the subsequent data communication.
 4. The system ofclaim 1, wherein the sensor electronics is configured to transition froma sleep mode to a communication mode upon activation.
 5. The system ofclaim 1, further including a receiver unit configured for receiving thedata packets over a paired communication link from the sensorelectronics.
 6. The system of claim 5, wherein the receiver unit isconfigured to establish the paired communication link with the sensorelectronics prior to receiving the data packets from the sensorelectronics.
 7. The system of claim 5, wherein the sensor electronics isconfigured to encode the data packets to generate encoded data packets,the sensor electronics further configured to communicate the encodeddata packets to the receiver unit.
 8. The system of claim 5, wherein thereceiver unit is configured to decode encoded signals received from thesensor electronics.
 9. The system of claim 1, wherein the data packetsincludes data points corresponding to the monitored analyte level over apredetermined time period.
 10. The system of claim 5, wherein thereceiver unit is configured to receive one or more data packets, andincludes an output unit for outputting data related to the received oneor more data packets, wherein the data is related to one or more glucoselevels.
 11. An apparatus, comprising: one or more processors; and amemory operatively coupled to the one or more processors, the memory forstoring instructions which, when executed by the one or more processors,causes the one or more processors to process signals generated from ananalyte sensor having a portion in fluid contact with interstitialfluid, to form data packets associated with the generated signals fromthe analyte sensor, to communicate the data packets with each datacommunication, the data packets including a current data point thatcorresponds to an analyte level of a current time period and at leastone previous data point that corresponds to at least one analyte levelof at least one previous time period, and if the current data point isnot successfully received, at a subsequent data communication, tore-transmit the current data point and the at least one previous datapoint with a new current data point.
 12. The apparatus of claim 11,wherein the at least one previous data point includes two consecutivedata points that corresponds to monitored analyte level of twoconsecutive previous time periods, one of the two consecutive previoustime periods immediately preceding the current time period.
 13. Theapparatus of claim 11, wherein the current data point is received andascertained from the subsequent data communication.
 14. The apparatus ofclaim 11, wherein the one or more processors is configured to transitionfrom a sleep mode to a communication mode upon activation.
 15. Theapparatus of claim 11, wherein the one or more processors is configuredto encode the data packets to generate encoded data packets for the datacommunication.
 16. The apparatus of claim 11, wherein the data packetsincludes data points corresponding to monitored analyte level over apredetermined time period.
 17. The apparatus of claim 11, furtherincluding a temperature sensor operatively coupled to the one or moreprocessors and configured to monitor temperature associated with theanalyte sensor, wherein the monitored temperature is used to adjust theprocessed generated signals.
 18. The apparatus of claim 17, wherein thetemperature sensor detects temperature level of an insertion site of theanalyte sensor to obtain a temperature reading, wherein the one or moreprocessors uses the temperature reading to adjust the processedgenerated signals.